Composite photoresist for pattern transferring

ABSTRACT

A composite photoresist structure includes an first organic layer located on a substrate, a sacrificial layer located on the first organic layer, and a second organic layer located on the sacrificial layer. The first organic layer is made of materials that can be easily removed by plasma. Therefore, the surface of the substrate will not be damaged while transferring a predetermined pattern onto the substrate.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a photoresist structure, and moreparticularly, to a photoresist structure suitable for sub-micron patterntransfers in semiconductor processes.

2. Description of the Prior Art

Generally, integrated circuit production relies on the use ofphotolithographic processes and etching processes to define variouselectrical elements and interconnecting structures on microelectronicdevices. With the coming of a generation of Ultra Large Scale Integrated(ULSI) Circuits, the integration of semiconductor devices has gottenlarger and larger. G-line (436 nm) and I-line (365 nm) wavelengths oflight have been widely used in photolithography processes. However, inorder to achieve smaller dimensions of resolution, wavelengths of lightused for photolithography processes have been reduced into deep UVregions of 248 nm and 193 nm. Nevertheless, the shorter the wavelengthsof light are, the thinner the photoresist layers are. The thinphotoresist layers might not be thick enough for blocking the etchingprocesses in the following fabrication. As a result, for aphotolithography process utilizing short wavelengths of light, it isnecessary to look for a photoresist structure suitable for lithographyprocesses and etching processes.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior artphotoresist structure. As shown in FIG. 1, a semiconductor wafer 10comprises a substrate 12, an anti-reflection layer 14, and a photoresistlayer 16. Because wavelengths of light used for exposure processes arerelated to the depth of focus (DOF), a required thickness of thephotoresist layer 16 depends on the wavelengths of light. Accordingly,the thickness of the photoresist layer 16 has to be thin enough so thatthe molecules in the surface of the photoresist layer have approximatelythe same focus as the molecules in the bottom of the photoresist layer.However, the photoresist layer 16 is used to be a hard mask on thesubstrate 12 in the following etching processes. For this reason, thethin photoresist layers might not be thick enough for blocking thefollowing etching processes.

Please refer to FIG. 2. FIG. 2 is a schematic diagram of another priorart photoresist structure used to overcome the above-mentioned problem.As shown in FIG. 2, a semiconductor wafer 20 comprises a substrate 22, asilicon oxynitride layer 24, an anti-reflection layer 26, and aphotoresist layer 28. Therein the silicon oxynitride layer 24 serves asa hard mask so that the photoresist layer 28 together with the siliconoxynitride layer 24 can block the etching processes in the followingfabrication. After the predetermined pattern of the mask is transferredonto the substrate 22, the silicon oxynitride layer 24, theanti-reflection layer 26, and the photoresist layer 28 are removed.However, the silicon nitride layer 24 is not easy to etch away. Thus,the process of removing the silicon nitride layer 24 usually causesdamage to the surface of the substrate 22.

In addition, methods used to overcome the above-mentioned problemfurther include bilayer photoresist technology (U.S. Pat. No. 6,323,287)and top surface image (TSI) technology (U.S. Pat. No. 6,296,989).However, both of the two methods require new photoresist materials. Forexample, the photoresist layer used in the TSI technology comprisessilicon-containing materials. Providing new photoresist materials willincrease production costs and increase complexity and difficulty ofprocesses. As a result, it is necessary to look for a photoresiststructure suitable for sub-micron pattern transfers in photolithographyprocesses and etching processes.

SUMMARY OF INVENTION

It is therefore a primary objective of the claimed invention to providea composite photoresist structure so as to solve the above-mentionedproblem.

According to the claimed invention, a composite photoresist structureincludes a first organic layer located on a substrate, a sacrificiallayer located on the first organic layer, and a second organic layerlocated on the sacrificial layer. The first organic layer is made ofmaterials that can be easily removed by plasma. Therefore, the surfaceof the substrate will not be damaged while transferring a predeterminedpattern onto the substrate.

It is an advantage over the prior art that the claimed inventionprovides a composite photoresist structure including a first organiclayer, an inorganic sacrificial layer, and a second organic layer. Athickness of the second organic layer can be adjusted according towavelengths of light sources used in exposure processes. Simultaneously,by adjusting thicknesses of the sacrificial layer and the first organiclayer, the composite photoresist structure is thick enough to blockfollowing etching processes. Thus, the claimed photoresist structure issuitable for sub-micron pattern transfers in semiconductor processes. Inaddition, the first organic layer is regarded as a hard mask and it iseasily removed by use of plasma. It is a further advantage that removingthe first organic layer will not damage the substrate.

These and other objectives of the claimed invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment, which isillustrated in the multiple figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a prior art photoresist structure.

FIG. 2 is a schematic diagram of another prior art photoresiststructure.

FIG. 3 is a schematic diagram of a composite photoresist structureaccording to the present invention.

FIG. 4A to FIG. 4F are schematic diagrams illustrating an etchingprocess utilizing the composite photoresist structure.

FIG. 5 is a schematic diagram of a composite photoresist structureaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 3. FIG. 3 is a schematic diagram of a compositephotoresist structure according to the preferred embodiment of thepresent invention. As shown in FIG. 3, a composite photoresist structure30 comprises a first organic layer 30 a, a sacrificial layer 30 blocated on the first organic layer 30 a, and a second organic layer 30 clocated on the sacrificial layer 30 b. The first organic layer 30 a andthe second organic layer 30 c both comprise organic materials. Thesacrificial layer 30 b comprises inorganic materials.

In particular, the first organic layer 30 a is made of low dielectricorganic materials, such as SiLK™. Additionally, the first organic layer30 a is also made of spin-on glass (SOG). Consequently, it is easy toremove the first organic layer 30 a by means of plasma, which includesoxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y),C_(x)H_(y)F_(z), or helium (He) plasma. The sacrificial layer 30 b ismade of inorganic anti-reflection materials such as silicon oxynitride(SiON) and silicon nitride (SiN). In addition, the sacrificial layer 30b is also made of materials used for conventional hard masks, such assilicon nitride and silicon oxide. Moreover, the second organic layer 30c is made of organic photoresist materials that include positivephotoresist materials and negative photoresist materials. Furthermore,the second organic layer 30 c is made of organic materials suitable forutilizing in the e-beam lithography process. Noticeably, the compositephotoresist structure 30 is suitable for any photolithography processesin the semiconductor fabrication. It should be known by one skilled inthe art that a thickness of each of the first organic layer 30 a, thesacrificial layer 30 b, and the second organic layer 30 c could beadjusted according to requirements of processes.

Please refer to FIG. 4A to FIG. 4F. FIG. 4A to FIG. 4F are schematicdiagrams illustrating an etching process utilizing the compositephotoresist structure 30. As shown in FIG. 4A, a semiconductor wafer 40comprises a substrate 42 and the composite photoresist structure 30formed on the substrate 42. The substrate 42 is a silicon substrate, ametal substrate or a dielectric layer. Firstly, as shown in FIG. 4B andFIG. 4C, an exposure process and a development process are performed totransfer a predetermined pattern onto the second organic layer 30 c.Then, using the second organic layer 30 c as an etching mask, a dryetching process is performed on the sacrificial layer 30 b in order totransfer the predetermined pattern in the second organic layer 30 c ontothe sacrificial layer 30 b. Besides, in another embodiment of thepresent invention, the predetermined pattern can be formed in the secondorganic layer by utilizing the e-beam lithography process.

As shown in FIG. 4D to FIG. 4F, utilizing the sacrificial layer 30 b tobe an etching mask, an anisotropic etching process is performed totransfer the predetermined pattern onto the first organic layer 30 b.Then, using the sacrificial layer 30 b and the first organic layer 30 aas an etching mask, an etching process is performed to transfer thepredetermined pattern in the first organic layer 30 a onto the substrate42. While etching the substrate 42, the sacrificial layer 30 b isremoved concurrently. After transferring the predetermined pattern ontothe substrate 42, the first organic layer 30 a is subsequently removed.Up to now, the predetermined pattern on the mask is thoroughlytransferred onto the substrate 42. The first organic layer 30 a isregarded as a hard mask, and its thickness can be adjusted in order toblock subsequent etching processes. Thus, the composite photoresiststructure 30 can be used in a photolithography process utilizing lightsources with wavelengths shorter than 248 nm in deep UV regions.Furthermore, conventional hard masks are generally made out of siliconnitride or silicon oxide, which are not easy to etch away. Hence, anacidic trough is required to remove the conventional hard masks.Conversely, it is easy to remove the first organic layer 30 a throughuse of plasma. Furthermore, removing the first organic layer 30 a willnot damage the substrate 42.

Please refer to FIG. 5. FIG. 5 is a schematic diagram of a compositephotoresist structure according to another embodiment of the presentinvention. As shown in FIG. 5, a composite photoresist structure 50comprises a first organic layer 50 a, a sacrificial layer 50 b locatedon the first organic layer 50 a, an anti-reflection layer 50 c locatedon the sacrificial layer 50 b, and a second organic layer 50 d locatedon the anti-reflection layer 50 c. The first organic layer 50 a is madeof low dielectric organic materials. In addition, the first organiclayer 50 a can be made of spin-on glass (SOG). It is easy to remove thefirst organic layer 50 a by use of plasma. The sacrificial layer 50 b ismade of materials used for hard masks such as silicon nitride andsilicon oxide. The anti-reflection layer 50 c is made of organicmaterials used for organic bottom anti-reflection coating such aspolyimide and the like. Additionally, the anti-reflection layer 50 c canalso be made of inorganic materials used for inorganic bottomanti-reflection coating such as silicon oxynitride (SiON). Theanti-reflection layer 50 c can prevent incident light from reflectingfrom the substrate to the composite photoresist structure 50. Thus, dueto the anti-reflection layer 50 c, forming a standing wave in the secondorganic layer 50 d is avoided. The second organic layer 50 d is made oforganic photoresist materials that comprise positive photoresistmaterials and negative photoresist materials. As mentioned above, thecomposite photoresist structure 50 can be utilized in anyphotolithography processes. It should be known by one skilled in the artthat a thickness of each of the first organic layer 50 a, thesacrificial layer 50 b, the anti-reflection layer 50 c, and the secondorganic layer 50 d could be adjusted according to requirements ofprocesses.

In comparison with the prior art, the present invention provides acomposite photoresist structure including a first organic layer, aninorganic sacrificial layer, and a second organic layer. A thickness ofthe second organic layer could be adjusted according to wavelengths oflight sources used in exposure processes. Simultaneously, by adjustingthicknesses of the sacrificial layer and the first organic layer, thecomposite photoresist structure is thick enough to blockensuing etchingprocesses. Thus, the claimed photoresist structure is suitable forsub-micron pattern transfers in semiconductor processes. As a result,the predetermined pattern of the mask can be accurately transferred ontothe semiconductor wafer, and a critical dimension (CD) is thereforecontrolled well. In addition, the first organic layer is regarded as ahard mask and it is easily removed through use of plasma. It is also anadvantage that removing the first organic layer will not damage thesubstrate.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bound of the appendedclaims.

1. A composite photoresist structure for transferring a pattern onto asurface to be etched, comprising: a first organic layer disposed overthe surface to be etched, and totally removed after a patterntransferring process; a sacrificial layer disposed on the first organiclayer; and a second organic layer disposed on the sacrificial layer,wherein the second organic layer is made of organic photoresist materialwhich is selected from the group consisting of positive organicmaterial, negative organic material, and a material suitable forutilizing in e-beam lithography process.
 2. The composite photoresiststructure of claim 1 wherein the surface is selected from the groupconsisting of a silicon surface, a metal surface, and a dielectric layersurface.
 3. The composite photoresist structure of claim 1 wherein thefirst organic layer is made of an organic material that is easy to betotally removed by means of plasma, thereby avoiding damage of thesurface to be etched during a photoresist removing process.
 4. Thecomposite photoresist structure of claim 3 wherein the first organiclayer is made of low dielectric organic materials.
 5. The compositephotoresist structure of claim 3 wherein the first organic layer is madeof SOG.
 6. The composite photoresist structure of claim 3 wherein theplasma is selected from the group consisting of oxygen (O₂), nitrogen(N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y), C_(x)H_(y)F₂, and helium(He) plasma.
 7. The composite photoresist structure of claim 1 whereinthe sacrificial layer is made of inorganic anti-reflection materials. 8.The composite photoresist structure of claim 1 wherein the sacrificiallayer is made of a material selected from the group consisting ofsilicon nitride, silicon oxide, and silicon oxynitride.
 9. The compositephotoresist structure of claim 1 wherein the second organic layer ismade of an organic photoresist material capable of absorbing light witha wavelength of 248 nm and the less.
 10. A photoresist structure fortransferring a sub-micron pattern onto a surface to be etched,comprising: a first organic layer disposed over a the surface to beetched, and totally removed after a pattern transferring process of thesub-micron pattern; a sacrificial layer disposed on the organic layer;an anti-reflection layer disposed on the sacrificial layer; and a secondorganic layer disposed on the anti-reflection layer, wherein the secondorganic layer is made of organic pbotoresist material which is selectedfrom the group consisting of positive organic material, negative organicmaterial, and a material suitable for utilizing in e-beam lithographyprocess.
 11. The photoresist structure of claim 10 wherein the surfaceis selected from the group consisting of a silicon surface, a metalsurface, and a dielectric layer surface.
 12. The pHotoresist structureof claim 10 wherein the first organic layer is made of an organicmaterial that is easy to be totally removed by means of plasma, therebyavoiding damage of the surface to be etched during a photoresistremoving process.
 13. The photoresist structure of claim 12 wherein thefirst organic layer is made of a material selected from the groupconsisting of low dielectric organic materials and SOG.
 14. Thephotoresist structure of claim 12 wherein the plasma is selected fromthe group consisting of oxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon(Ar), C_(x)F_(y), C_(x)H_(y)F₂, and helium (He) plasma.
 15. Thephotoresist structure of claim 10 wherein the sacrificial layer is madeof a material selected from the group consisting of silicon nitride andsilicon oxide.
 16. The photoresist structure of claim 10 wherein theanti-reflection layer is made of organic anti-reflection materials. 17.The photoresist structure of claim 16 wherein the anti-reflection layeris made of polyimide.
 18. The photoresist structure of claim 10 whereinthe anti-reflection layer is made of inorganic anti-reflectionmaterials.
 19. The photoresist structure of claim 18 wherein theanti-reflection layer is made of a material selected from the groupconsisting of silicon nitride and silicon oxynitride.
 20. Thephotoresist structure of claim 10 wherein the sacrificial layer isremoved during a predetermined pattern being transferred to the surfaceto be etched, while the first organic layer is removed after thepredetermined pattern is transferred into the surface to be etched. 21.The photoresist structure of claim 10 wherein the second organic layeris made of an organic photoresist material capable of absorbing lightwith a wavelength of 248 nm and the less.